The Cost column of the Profitability report is driven by transactions which post to COGS account. Costs like expenses are typically debited as they are incurred. However, if a COGS account is credited instead, it reverses the sign because it is a deduction to cost.
An item receipt was calculated with a Purchase Price Variance and the account user selected in the Purchase Price Variance field (under the Accounting tab of the item record) is a COGS type of account.
Debit: Inventory Received Not Billed __________$10.00
Credit: Purchase Price Variance – COGS _________$10.00
Once a transaction for an item posts to COGS account it is inevitable that a $10.00 will display under the Cost column of the report. But because the COGS account is credited, it will appear as negative to show that this is a deduction to item's cost.